1. Field of the Invention
The present invention relates to optical discs and in particular, to an optical disc in which an electromagnetic coupling module having a wireless integrated circuit (IC) chip for use in a radio frequency identification (RFID) system is disposed.
2. Description of the Related Art
Recently, digital versatile discs (DVDs) have become very popular as media capable of recording a large amount of data, such as video and audio data. With the desire to record longer video data having higher image quality, the development of optical discs whose light source is a blue semiconductor laser is rapidly advancing, and one example of this type of optical discs is a Blu-ray disc (BD) that is currently commercially available.
When a portable recording media is capable of easily storing high-quality digital contents, the protection of the copyright of the digital contents becomes very important. BDs perform control so as to prevent unauthorized discs from being played by causing a player to read a unique ID recorded in the innermost area of a signal recordable region, called a burst cutting area, for each disc as a bar-code pattern. However, techniques for creating unauthorized discs are rapidly advancing, such that more robust measures for copyright protection are desired.
To address this issue, a DVD having a structure in which an RFID tag is incorporated to prevent unauthorized duplication is disclosed in Japanese Unexamined Patent Application Publication No. 9-245381 and Japanese Unexamined Patent Application Publication No. 2006-92630. In Japanese Unexamined Patent Application Publication No. 9-245381, an antenna pattern is provided in an area that is adjacent to the central hole and that does not include a reflective film provided therein. This limits the size of the antenna pattern, such that a relatively large gain cannot be obtained and the reading distance by an RFID reader/writer is undesirably small. One possible solution is to provide the antenna pattern on the back surface of a signal recordable region at which a reflective film is provided. However, with this approach, if the antenna pattern and the reflective film overlap, communications are adversely affected.
In Japanese Unexamined Patent Application Publication No. 2006-92630, an RFID tag is provided which has a slot antenna structure in which a slit is provided on each of an inner portion and an outer portion of a reflective film that are not disposed in a signal recordable region. However, because slot antennas have relatively high impedances, it is difficult to perform matching to the impedance of a wireless IC chip of the RFID. As a result, a problem occurs in which a sufficient antenna gain cannot be obtained.